Depends on the Airport terminus
As mentioned in Auckland Transit Gathers Pace Auckland Transport has released tender documents for the Botany to Airport Mass Transit Line (known as the Southern Airport Line) to be completed 2020 (Airport to Manukau) and 2023 (Botany Interchange) respectively. While the Northern Airport Line (Airport to City Centre then onwards as the North Shore Line (Central Line under the Congestion Free Network MK2)) is set to be Light Rail the Southern Airport Line is set to be a bus rapid transit system like the current Northern Busway.
The cost for a bus way from the Airport to Botany is about $380 million while Light Rail would be the same price as the Airport Line at $1.2 billion approx. I can understand Greater Auckland’s concerns making the Southern Airport Line full Light Rail right off the bat given expense and time (add another few years to construction times) but a fellow Tweeter did raise a concern about the Airport industrial complex along State Highway 20A being out of reach of the Southern Airport Line.
Source: Auckland Transport
Most of the workers for the Airport industrial complex come from Southern Auckland (with a decent portion coming from West Auckland). While the Southern Airport Line does reach the Airport Business Park it does not reach the industrial complex further north meaning the Line is only doing half its job. Coincidentally a question on where the trains for the Northern Airport Line would be stored comes to mind and while one depot would be near the City Centre another one would need to be near the Airport.
If successful the land would be converted from rural to industry (it was converted)
Enter the Puhinui Gateway industrial complex recently formed along State Highway 20B thanks to the Unitary Plan. Puhinui Gateway is newly zoned Light Industrial land on the southern side of State Highway 20B. Currently it is fields but in time it will be industry to support the Airport and Wiri complexes. The spot given the proximity to the Airport Terminus would be ideal forming a second depot for the Northern Airport Line but it then does present a prime opportunity for the Southern Airport Line.
The Southern Airport Line intersects Puhinui Station which has the Southern and Eastern Lines (and later Inter City trains under the Regional Rapid Rail scheme) allowing near universal access from those who can access the rail network or Northern Busway. The Southern Airport Line also intersects Manukau Bus/Train Station which is the primary South Auckland commuter bus hub and southern base for the inter-city bus network. This means lots of people and potentially lots of people transferring off the heavy rail trains, busses and inter city busses to the Southern Airport Line heading to the Airport (or reverse). These people also include those workers who I had mentioned earlier.
With potential demand, intersecting of two major transit hubs, the placement of a second depot in the Puhinui Gateway area to service the Northern Airport Line and Southern Auckland workers working in the Airport industrial complex this is the compromise I was thinking of:
The Southern Airport Line is Light Rail from Manukau to the Airport and arcs around at the Airport Terminus allowing a straight run through to the Northern Airport Line (as shown below)
Source: Auckland Transport and NZTA
Meaning? A train from Manukau to the Airport on the Southern Airport Line would continue straight through at the Airport Terminal onto the Northern Airport Line and its trip to the City Centre eliminating a clumsy second transfer for Southern Auckland workers working at the Airport industrial complexes (the first is at either Manukau or Puhinui)(see the Green thick line by AT, Council and NZTA above this bend around). Given the second depot would be located in the Puhinui Gateway area extending the Light Rail from the Airport to Manukau just makes sense. The Manukau to Botany section can continue to be bus until demand is sufficient for Light Rail.
Southern Auckland
Source: Greater Auckland
In short:
The a train from the Northern Airport Line would be able to continue onto the Southern Airport Line and complete its trip at Manukau before doing the reverse back to the City Centre. It would be like post City Rail Link where currently terminating services at Britomart can run through the CRL improving efficiency and capacity of the network.
I think this is good compromise for the Southern Airport Line allowing capacity, efficiency and connectivity for Southern Auckland workers to their employment places without the major expense of a full LRT line to Botany.
What do you think?
Source: The Spinoff
Source: Greater Auckland
Talking Southern Auckland 
“Rapid Regional Rail
Source: Auckland Transport”
Uuuuuh, don’t think so champ.
Changed
Thanks for the heads up
Yep, it just makes sense…….for now, leaving wriggle room for changes as expanding need dictates. Be very mindful of the effect rail has had on Auckland commuters with demand growth beyond all expectations. The movie Field of Dreams springs to mind, If you build it they will come.
I think the relavent word in this post is “COMPROMISE”. Let’s face it in a perfect world we would have heavy rail to the airport but because we need to concentrate our resources to building a number of light rail services we need to compromise, as Auckland is so good at, and accept an extension of the Mt Roskil proposed light rail to the airport.